U.S. mass shooters exploited gaps, errors in background checks

Most mass shooters in the U.S. acquired the weapons they used legally because there was nothing in their backgrounds to disqualify them, according to James Alan Fox, a criminologist with Northeastern University who has studied mass shootings for decades. But in several attacks in recent years gunmen acquired weapons as a result of mistakes, lack of follow-through or gaps in federal and state law. Not all gun purchases are subject to a federal background check system. Even for those that are, fed